simple rain tutorial
(sorry its hard to see, but rain is kinda hard to see)
step 1: make your 3 colors of rain, a medium shade, a light shade and a dark shade
step 2: use the medium shade and scribble using the airbrush on a low size
step 2: add the highlights to the rain by using the light shade, use less then the base (the medium shade)
step 3: add the low-lights to the rain by using the dark shade, use less then the base (the medium shade)
at the bottom you can see what rain looks like in a larger proportion, his does look better when you can see the ends
example of rain, click to see bigger
http://www.chickensmoothie.com/oekaki/image/image.php?id=163811&size=gallery&format=jpg&rev=2